Dc-coupled switching in an ac-coupled environment

ABSTRACT

An example system includes input circuitry configured to obtain first data corresponding to first signals on a communication channel, with the first data having a first frequency that is less than a predefined frequency; and sampling circuitry configured to sample the first data to produce second data having a second frequency that is greater than or equal to the predefined frequency. The example system also includes switching circuitry configured to support AC-coupled data having a frequency that is greater than or equal to the predefined frequency, with the switching circuitry being configured to receive the second data and to forward the second data; and output circuitry to receive the second data and parametric data representing non-information signal content, to produce third data based on the second data, and to produce, based on the third data and the parametric data, second signals for output from the system.

TECHNICAL FIELD

This specification relates generally to communicating data transmittedat frequencies through a switch matrix that supports frequencies greaterthan a predefined frequency.

BACKGROUND

A signal includes informational content and characteristics other thaninformational content. For example, an optical signal may have anoptical power level, which is a measure of the energy delivered by theoptical signal per unit of time. In another example, an electricalsignal may have a signal-to-noise ratio, which reflects the relativeamounts of signal and noise in a transmission. These signalcharacteristics that do not represent the informational content of thesignal are referred to as parametric information, and may be representedby data, called parametric data. The informational content of the signalmay be represented by informational content data.

The informational content data and the parametric data may betransmissible at frequencies, or data rates, that are not supported bysome circuit elements.

SUMMARY

An example system includes input circuitry configured to obtain firstdata corresponding to first signals on a communication channel, with thefirst data having a first frequency that is less than a predefinedfrequency; and sampling circuitry to sample the first data to producesecond data having a second frequency that is greater than or equal tothe predefined frequency. The example system also includes switchingcircuitry to support AC-coupled data having a frequency that is greaterthan or equal to the predefined frequency, with the switching circuitrybeing configured to receive the second data and to forward the seconddata; and output circuitry to receive the second data and parametricdata representing non-information signal content, to produce third databased on the second data, and to produce, based on the third data andthe parametric data, second signals for output from the system. Theexample system may include one or more of the following features, eitheralone or in combination.

The sampling circuitry may be configured to encode the first data at thesecond frequency to produce the second data. The output circuitry may beconfigured to decode the second data to produce the third data. Thethird data may have a third frequency that is less than the predefinedfrequency. The third frequency may be the same as the first frequency orhave any other appropriate frequency.

The parametric data may represent non-informational signal content ofthe first signals. The sampling circuit may be configured to encode theparametric data at a third frequency that is greater than or equal tothe predefined frequency to produce encoded parametric data. Theswitching circuit may be configured to receive the encoded parametricdata, and to forward the encoded parametric data to the outputcircuitry. The output circuitry may be configured to decode the encodedparametric data to produce the parametric data. The parametric data mayhave a fourth frequency that is less than the predefined frequency.

The switching circuitry may comprise a first switch to receive thesecond data and to forward the second data to the output circuitry; anda second switch to receive the parametric data and to forward theparametric data to the output circuitry. The parametric data representsnon-informational signal content of the first signals. The first switchand the second switch may be controllable independently. The outputcircuitry may comprise a selector circuit to receive the parametric datafrom a source other than the switching circuitry, and to select theparametric data for use by the output circuitry to produce the thirddata. The second signals may be based on, or identical to, the firstsignals both informationally and parametrically. The first frequency andthe second frequency may be each non-zero AC frequencies. The firstfrequency is zero and the second frequency may each be a non-zero ACfrequency.

An example method comprises obtaining first data corresponding to firstsignals on a communication channel, with the first data having a firstfrequency that is less than a predefined frequency; sampling the firstdata to produce second data having a second frequency that is greaterthan or equal to the predefined frequency; receiving, at switchingcircuitry, the second data and forwarding the second data, where theswitching circuitry is configured to support AC-coupled data having afrequency that is greater than or equal to the predefined frequency;producing third data based on the second data; and producing secondsignals for output based on the third data and the parametric data. Thisexample method may also include one or more of the foregoing featuresassociated with the example system, as appropriate.

Any two or more of the features described in this specification,including in this summary section, can be combined to formimplementations not specifically described herein.

The systems and techniques described herein, or portions thereof, can beimplemented as/controlled by a computer program product that includesinstructions that are stored on one or more non-transitorymachine-readable storage media, and that are executable on one or moreprocessing devices to control (e.g., coordinate) the operationsdescribed herein. The systems and techniques described herein, orportions thereof, can be implemented as an apparatus, method, orelectronic system that can include one or more processing devices andmemory to store executable instructions to implement various operations.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of components of an example system thatincorporates an implementation of the switch matrix system describedherein.

FIG. 2 is a block diagram of components of an example instrument modulefor transmitting parametric data from an instrument module to abackplane.

FIG. 3 is a block diagram of components of an example parametric dataswitch matrix that may be included in the example system.

FIG. 4 is a block diagram showing an example of an active control loopfor controlling parametric information on channels.

FIG. 5 is a block diagram showing, conceptually, examples of circuitcomponents for adjusting frequencies of signals.

Like reference numerals in different figures indicate like elements.

DETAILED DESCRIPTION

Described herein are example systems that include multiple instrumentmodules. Each of the instrument modules is configured to communicatewith one or more devices being tested by the system, and also tocommunicate with other instrument modules that are part of the system. Adevice being tested is referred to herein as a device under test (DUT)or a unit under test (UUT). Each instrument module is part of acommunication (e.g., test) channel (or simply, “channel”), over whichcommunications occur. The instrument modules communicate with each otherover one or more transmission media on a backplane or other appropriatestructure to which the instrument modules interface. For example, theinstrument modules may communicate via one or more serial buses on thebackplane or via an Ethernet-based network.

Switching circuitry, which may reside on the backplane or at anotherappropriate location in the system, directs communication data to andfrom different instrument modules/communication channels. The switchingcircuitry enables, among other things, any appropriate communicationdata to be transmitted from one channel to multiple channels (via theirrespective instrument modules), from multiple channels to one channel,or from one channel to another, different channel. The communicationprocess may include replicating all or part of the communication data asclosely as possible on one or more other channel(s), or processing thecommunication data and transmitting the resulting processedcommunication data, as appropriate. The communication process may alsoinclude substituting user-provided, or other, communication data forexisting communication data, where appropriate.

The communication data may include data that represents bothinformational content and data that represents one or more signalcharacteristics other than informational content. Informational contentincludes the information being transmitted in a signal optically orelectrically (e.g., a bit stream). Data that represents theinformational content is referred to herein as informational contentdata. Data that represents one or more signal characteristics other thaninformational content is referred to herein as parametric data. Forexample, in some implementations, an instrument module may receive aninput signal. The input signal may be optical or electrical; however,for illustration, an optical signal is received in this example. Theoptical signal may represent, for example, test data from a UUT orcommands from a host computing system to control testing. The opticalsignal may be received over one or more optical fibers interfaced to, orotherwise in communication with, the system. The optical signalrepresents information, as indicated, but also has othercharacteristics. For example, the optical signal may have an opticalpower level, a signal-to-noise ratio, a modulation amplitude, anextinction ratio, a wavelength, a rise time, a fall time, a slew rate,or any other characteristic relating to a wave or the wave's shape. Theinstrument module receives the optical signal and converts the opticalsignal into an electrical (e.g., digital) signal comprising datarepresenting the informational content of the optical signal (e.g., thetest data, commands, etc.). The instrument module also captures theother characteristics—the parametric information—associated with theoptical signal, and generates parametric data representing thisparametric information. Both the informational content data and theparametric data may constitute the communication data referred to above,and may be transmitted among the instrument modules and associatedcommunication channels.

As indicated above, the input signal may also be an electrical signal.The electrical signal may be a digital signal or an analog signal, forexample. Electrical signals also have associated parametric information,such as signal-to-noise ratio, amplitude values, and so forth. Thus, aninstrument module may receive an electrical signal—which may be analogor digital—generate a digital signal comprising informational contentdata representing the received electrical signal, and generateparametric data representing the parametric information associated withthe electrical signal. The processing described herein for the resultinginformational content data and parametric data is substantially the sameregardless of whether the original input signal is optical orelectrical. For this reason, the following addresses receipt of anoptical signal only, with the understanding that the processingdescribed applies equally in cases where the original input signal iselectrical. Also, individual channels may contain more than oneinformational stream and, although the processing described hereinrelates to individual streams per channel, the processing describedherein likewise applies to multiple streams per channel.

In some implementations, the switching circuitry comprises a firstswitching circuit and a second switching circuit. The first switchingcircuit is referred to as the signal switching circuit or the digitaldata switch matrix (DDSM), since this switching circuit provides, ordistributes, to various instrument modules/communication channels, theinformational content data representing the original signal. In someimplementations, the DDSM is a single part that is a full cross-pointswitch and that is configured to operate on high-speed digital data. Inan example, high-speed data may include data that is transmitted on theorder of gigabits-per-second (Gb/s); however, the DDSM is not limited touse with such data transmission speeds. The DDSM may be configured toreceive data on one channel's input and to reproduce that data on anynumber of desired outputs. In some implementations, the DDSM does notcapture any data in memory; it simply makes a copy of the data on eachdesired output. In some implementations, the DDSM may store data inon-board memory. In some implementations, the DDSM has input buffers andre-drivers. In some implementations, either the PDSM or the DDSM is notused.

The second switching circuit is referred to as the parametric switchingcircuit or the parametric data switch matrix (PDSM), since thisswitching circuit provides, or distributes, to various instrumentmodules/communication channels, parametric data representing one or moresignal characteristics other than informational content. In someimplementations, the PDSM is a virtual switch matrix that enableshigh-speed serial communication of individual channels' parametric datatransmitted among instrument modules in real-time. The systemarchitecture supports parametric data of all appropriate typesincluding, but not limited to, optical power levels, signal-to-noiseratio, modulation amplitude, extinction ratio, wavelength, rise time,fall time, slew rate, or any other characteristic relating to a wave orthe wave's shape. In some implementations, the use of the PDSM isoptional. In such implementations, a host computing system can simplyselect a desired output parameter (e.g., power level) for each channeland ignore the measured parameter at the input and received by the DDSM.The selected data can be transmitted to multiple channelssimultaneously. In some implementations, the PDSM is configured toobtain parametric data from one or more instrument modules and isconfigured to transmit any module's port and channel parametric data toany other module's port and channel. This operation may be done on acontinual basis as the data in question is changing. The PDSM may obtainparametric data from both input and output ports.

Some implementations may employ a different switch matrix configurationthan that described here. For example, in some implementations, a singleswitch matrix may handle both the informational content data and theparametric data. For example, a single hardware switch may include bothPDSM and DDSM functionality.

The DDSM and the PDSM may be configured, or controlled, to operate inparallel. For example, the DDSM may be configured to transmitinformational content data at the same time as the PDSM transmitsparametric data, and the PDSM may be configured to transmit parametricdata at the same time as the DDSM transmits informational content data.In some implementations, the DDSM and the PDSM may be configured, orcontrolled, to operate independently or in concert to distribute theirrespective data to appropriate communication channels of the instrumentmodule.

In an example operation, an example instrument module #1 may receive aninput optical signal, convert that optical signal into informationalcontent data (e.g., a digital signal) representing the informationalcontent of the optical signal, and, during the conversion process,obtain parametric data representing the optical power of the opticalsignal (a non-informational characteristic of the optical signal). Theinformational content data and the parametric data may be sent overappropriate transmission media from the instrument module to theswitching circuitry (e.g., the informational content data to the DDSMand the parametric data to the PDSM). The switching circuitry, in thisexample, may be configured, e.g., by a host computing system, to providethe informational content data to example instrument modules #2, #3, and#4, and to provide the parametric data to example instrument modules #4,#5, and #6. Instrument module #4 may use both the informational contentdata and the parametric data to replicate, on its output communicationchannel, the optical signal originally received by instrument module #1.That is, the optical signal output by instrument module #4 may begenerated using the informational content data and the parametric datato have the same informational content and non-informationalcharacteristics (e.g., optical power) as the optical signal received byinstrument module #1. Instrument modules #2 and #3 may output an opticalsignal representing the informational content data and having anyappropriate parametrics, the data for which may be stored in therespective instrument modules or received from elsewhere. Instrumentmodules #5 and #6 may use the received parametric data to generateoptical signals having the same optical power as the optical signalreceived by instrument module #1. The informational content data used togenerate the informational content of the optical signals output byinstrument modules #5 and #6 may be obtained from any appropriatesource. Other examples of functionalities available through theinstrument modules are provided below.

In some implementations, the switching circuitry (e.g., the PDSM and/orDDSM) does not process data, but rather is only configurable to transmitdata from one location to another location. In some implementations, theswitching circuitry may include on-board intelligence that enablesprocessing of the data prior to output from the switching circuitry. Inany case, processing device(s) either on, or off, the backplane, mayprocess the informational content data and/or the parametric data priorto distribution by the switching circuitry or following distribution bythe switching circuitry. Processing may include, but is not limited to,changing the content of the data, changing a timing of the data,changing packet headers for the data, and so forth. Therefore, ratherthan providing the informational content data and the parametric datareceived, the switching circuitry may provide modified versions of thatdata to the various instrument modules/transmission channels. In someimplementations, the switching circuitry may substitute designatedinformational content data and/or parametric data for different data,where the different data may be specified by a processing device, suchas the host computing system, based on programmatic input.

FIG. 1 shows components of example system 10 that incorporates anexample switch matrix system. Notably, however, the switching matrixsystem described herein is not limited to use in the context of testingor to use with the example system described herein, but rather may beused in any appropriate technical context, including outside of atesting environment. In FIG. 1, the dashed lines represent,conceptually, potential signal paths between components of the system.In this regard, in some implementations, the host computing system doesnot communicate directly with the instrument modules. Rather, there is alocal bus handled by a field programmable gate array (FPGA) on thebackplane that handles communication between the instrument modules andthe host computing system. In some implementations, the FPGA thathandles the communications is the same FPGA that implements the PDSM.

System 10 includes a test arrangement 11 and a host computing system 12.Test arrangement 11 may include interface(s) to one or more UUTs (notshown) on which tests are performed, and host computing system 12communicates with components thereof to control testing. For example,host computing system 12 may download test program sets to instrumentmodules on the test arrangement, which then run the test program sets totest UUTs in communication with the test arrangement. Host computingsystem 12 may also send, to instrument modules in the test arrangement,instructions, test data, and/or other information that is usable by thecorresponding instrument module to perform appropriate tests on a UUTinterfaced to the test arrangement. In some implementations, thisinformation may be sent via a computer network. Host computing system 12may configure the DDSM and the PDSM based on user-provided, or other,programmatic inputs. The programming may specify switch configurationswithin the DDSM and the PDSM, or other appropriate operations orconfigurations. The DDSM and PDSM may be programmed and reprogrammed inreal-time, as appropriate. In some implementations, the foregoinginformation may be sent via an optical network comprised of fiber opticlines that transmit optical signals between the instrument modules andthe computer. Conversions between optical and electrical signals may beperformed by the host computing system and by the respective instrumentmodules, as described herein. In some implementations, the foregoinginformation may be sent via a computer network, such as a local areanetwork (LAN) or a wide area network (WAN).

In the example of FIG. 1, system 10 includes multiple instrument modules13A to 13N, each of which may be configured, as appropriate, to performone or more of the functions described herein. Although only fourinstrument modules are depicted, the system may include any appropriatenumber of instrument modules, including those residing outside of testarrangement 11. In some implementations, each instrument module may beconfigured to output test signals to test a UUT based, e.g., on dataprovided by the host computing system, and to receive signals from theUUT. Different instrument modules may be configured to perform differenttests and/or configured to test different UUTs. The signals received mayinclude response signals that are based on the test signals and/orsignals that originate from the UUT that are not prompted by (e.g., arenot in response to) test signals. In some implementations, there may beelectrical connections between the UUT and the instrument modules, inwhich case the test data and response signals may be sent electrically.In some implementations, there may be optical connections between theUUT and the instrument modules, in which case the test data and responsesignals may be sent optically. In some implementations, there may bedirect fiber optic lines/links between the UUTs and the instrumentmodules, over which optical signals are transmissible. In someimplementations, there may be an optical network between the UUTs andthe instrument modules, over which optical signals are transmissible. Insome implementations, there may be a combination of optical andelectrical transmission media between the instrument modules and theUUTs. In some instances the UUT may only interface with instrumentmodules through the DDSM or PDSM.

Each instrument module may include input circuitry (e.g., an interfacecard) for receiving signals from one or more UUTs or other appropriatesignal source(s). Each instrument module may include output circuitryfor outputting signals to a communication channel defined by theinstrument module. In some implementations that employ opticalcommunications, each instance of the input circuitry includes aninterface circuit configured to receive an optical signal, configured toconvert the optical signal to an electrical (e.g., a digital) signalcomprising informational content data, configured to obtain parametricinformation about the optical signal before, during, or after theconversion process, and configured to obtain parametric data based onthe information (e.g., to generate digital data representing theparametric information). In an example, the parametric information maybe measured by the interface circuit and converted to digital data bythe interface circuit or other appropriate logic. In someimplementations, the interface circuit may be implemented using adevice, such as an FPGA, an application-specific integrated circuit(ASIC), or other appropriate hardware.

In some implementations, one or more instrument modules include one ormore optical interfaces that are designed to support 850 nanometers (nm)multi-mode optical communication from 1 Gb/s to 12 Gb/s or higher. Insome implementations, other types of optical interfaces may be used, orno optical interfaces may be used.

FIG. 2 shows an example implementation of circuitry 27 that may beincluded in an instrument module, such as 13A. In this example,instrument module 13A interfaces to a UUT 31 and exchanges test andresponse signals with that UUT. In this example instrument module 13Aincludes sixteen ports, of which two, 32 and 33, are shown. Each portincludes a transmit channel (“TX Chan”) 35 and a receive channel (“RXChan”) 36. The receive channel is part of the input circuitry, and isconfigured to receive signals from the UUT or elsewhere. The transmitchannel is part of the instrument module's output circuitry, and isconfigured to output signals to the UUT or elsewhere. Circuitry 27includes parametric measurement circuits, an example of which is 37. Inthis example, two parametric components, A and B (e.g., optical powerand wavelength, respectively), are measured. Therefore, there is onecorresponding parametric measurement circuit for each transmit andreceive channel. That is, one parametric measurement circuit for achannel measures component A and one parametric measurement circuit forthat channel measures component B. Parametric data representing thoseparametric components is sent from each channel to multiplexers 38 and39—one for each parametric component, A and B. Multiplexers 38 and 39each select data from channels designated, e.g., by the host computingsystem. Multiplexer 40 selects whether to provide parametric data forcomponent A or for component B to the serial bus transmission circuit41, which passes that data to backplane 42. Circuitry 27 also includesdecoders—one for each channel, of which two, 44 and 45, are shown. Thesedecoders transmit, to the input circuitry, information that is usable toadjust parametric data (via circuits 46 and 47) at the various ports.

Referring also to FIG. 1, the instrument modules may be interconnectedthrough backplane 42 or any other appropriate electrical or mechanicalmechanism. For example, instrument modules 13A to 13N may mechanicallyinterface, e.g., plug into, backplane 42 of FIG. 1. Backplane 42 mayinclude one or more transmission media over which communications passamong the various instrument modules. For example, the transmissionmedia may be, or include, one or more serial buses such as a peripheralcomponent interconnect express (PCIe) bus, Ethernet cable, or otherappropriate media. In the case of a PCIe bus, the parametric data may beencapsulated in PCIe bus packet format and transmitted from instrumentmodule logic (e.g., an FPGA) to the PDSM. In some implementations,different parametric data types may be stored in different packets. Insome implementations, the PDSM decodes incoming PCIe bus packets andstores the decoded parametric data in data-type-specific random accessmemory (RAM), which may also reside on the backplane and which may beaccessed by the instrument modules and the host computing system. Busprotocols other than PCIe and other types of encapsulation may be used.

Communications among the instrument modules pass through switchingcircuitry 28 which, as described herein, includes one or moreprogrammable switching matrices (e.g., the PDSM and DDSM) in someimplementations. Switching circuitry 28 is configurable to receiveinformational content data and parametric data, and to distribute theinformational content data and parametric data among the instrumentmodules. As explained, informational content data received from aninstrument module may be provided to one or more of the samecommunication channels, or to one or more different communicationchannels. Parametric data received from an instrument module may beprovided to one or more of the same communication channels, or to one ormore different communication channels. In some implementations, some ofthe informational content data may be sent to one set of channels, andsome of the parametric data may be sent to another set of channels, withthe first and second sets overlapping, at least in part. In someimplementations, the informational content data and the parametric datamay be sent to different numbers of channels or to the same number ofchannels. Basically, any routing that is appropriate may be implemented.In some implementations, instrument modules may receive data from theswitching circuitry, manipulate that data, and send the data back to theswitching circuitry. Example instrument module functionalities aredescribed below.

In this regard, in some implementations, instrument modules in thesystem may vary in capabilities. In an example, an instrument module,such as instrument module 13A of FIG. 1, receives an input signal—whichmay be an optical signal or an electrical signal—and separates the inputsignal's data component (bit stream) from the input signal's parametriccomponent. The system processes each component separately. The systemalso supports the testing of each signal's data and parametriccomponents, as well as the retransmission of these components, e.g., toanother instrument module through an appropriate switch. In someimplementations, the system is configured so that, through appropriateprogramming, the bit stream on a channel may be reproduced on any otherchannel output, and that bit stream may have output parameters that canbe specified programmatically in absolute terms or relative to one ormore references, such as the parameters of another channel.

As explained, on some implementations, switching circuitry 28 mayinclude a first switch (the DDSM 29) to handle distribution of theinformational content data, and a second switch (the PDSM 30) to handledistribution of the parametric data. Each switch 29 and 30 may beprogrammable and/or under control of host computing system 12 in themanner described herein. In some implementations, as noted, each switch29 and 30 may, or may not, have on-board intelligence that enablesprocessing its respective data prior to output to the instrumentmodules/communication channels. In some implementations, the DDSM isimplemented using a cross-point switch matrix; and, in someimplementations, the PDSM is implemented using an FPGA. In someimplementations, the DDSM is implemented using a cross-point switchmatrix that receives and forwards data without performing any processingon the data; and, in some implementations, the PDSM is implemented usingan FPGA that receives and forwards data and is also capable ofperforming processing on the data. However, hardware other than thatdescribed herein may be used to implement the DDSM and the PDSM. TheDDSM and/or the PDSM may be capable of processing data.

An example implementation of PDSM 30 is shown in FIG. 3. PDSM 30includes an input interface 50 for passing data received (RX) from aninstrument module 51, and for passing data to be transmitted (TX) datato the instrument module. A decoder 52 (one for each RX channel) decodesparametric data passed as PCIe packets to the PDSM, and outputsparametric data to a input demultiplexer, an example of which is 53.Each input demultiplexer (e.g., 53) receives all parametric datacomponents for the same input or output interface from all ports of theinstrument module and outputs those parametric data components toparametric data RAM, an example of which is 55. That data is output fromRAM, at an appropriate time, to one or more multiplexers, an example ofwhich is 56. Control over the output may be implemented by a hostcomputing system. The output multiplexer sends the parametric data, asappropriate, to a TX output for transmission to an instrument module orretransmission back to the switch. As shown, the PDSM is implementedusing an FPGA in this example.

Referring back to FIG. 1, a separate processing device, which may or maynot reside on the backplane, may perform processing before, during, orafter distribution implemented by the switches. In some implementations,processing may be directed by, or under control of, host computingsystem 12, which is described below. In some implementations, theprocessing may be performed in the instrument modules. In someimplementations, network 22 communicates through transmission media andlogic on the backplane 42 with instrument the modules.

In some implementations, host computing system 12 communicates with theinstrument modules via the backplane over a network 22, which may be anappropriate Ethernet-based communication network, an appropriate opticalnetwork, a wireless network, or some combination thereof. Thus, in someimplementations, network 22 may be, or include one or more opticalnetworks, including fiber optic links between the host computing systemand the instrument modules In some implementations, network 22 may be,or include, a LAN, wide area network (WAN), or a combination thereof. Insome implementations, network 22 may be, or include, a combined opticaland electrical network between the host computing system and instrumentmodules.

In the example of FIG. 1, system 10 also includes one or more interfaces16 that connects, optically, electrically and/or mechanically, tocomponents of test arrangement 11, such as the instrument modules. Theinterface(s) each define one or more sites 21, which may include pins,traces, or other points of electrical, optical, and/or mechanicalconnection to which one or more UUTs may connect—e.g., one UUT per site.Test signals, response signals, and other information pass over thesites between the UUT and instrument modules 13A to 13N. Connectionsbetween the instrument modules and the UUTs may be optical, electrical,or a combination thereof. In some implementations, each instrumentmodule may include a separate interface, e.g., an optical interface,that connects, through optical transmission media, directly to a UUT. Inan example implementation, the system supports up to ten modules—eachhaving sixteen channel inputs and sixteen channel outputs—that plug intoa backplane, such as backplane 42. Other implementations, however, mayhave different numbers of modules, channels, ports, and the like. Thebackplane includes hardware to implement the switch matrix functionalitydescribed herein (e.g., the switching performed by the DDSM and thePDSM). As described, the example system may be configured to capture allinformation about a signal at an input and to reproduce that same signalat the output. This includes the informational content data component aswell as parametric components, such as the power levels, waveform, andthe like.

In an example, the switching circuitry may be configured to connect asignal from one channel to another channel, and to preserve the powerlevel of the signal on that other channel. In an example operation, theDDSM passes data for that signal to the other channel/instrument module.The PDSM provides the instrument module that controls the output signalwith the measured power levels of the input channel. The instrumentmodule then produces a signal having the informational content of theinformational content data and having the power level represented by theparametric data. The same concepts can be used for margin testing. Forexample, a user may want to emulate an optical fiber having a 2 decibel(dB) loss. The user can program the output of an instrument module toalways produce a signal having an output power level that is 2 dB lessthan a power level measured at its input. The system also supportsadding gain, e.g., programming the output of an instrument module toalways produce a signal having an output power level that is 2 dBgreater than the power level measured at an input.

In some implementations, the host computing system can configure thePDSM so that parametric data from any appropriate port and channel canbe sent to any other appropriate port and channel. The host computingsystem can also program the system so that parametric data is not sentto any given port or channel on a per channel basis. After aconfiguration is defined, the PDSM may send parametric data encapsulatedin PCIe packet format to all designated instrument modules, ports, andchannels. In some implementations, the configuration can be modified inreal-time.

In some implementations, each instrument module may be configured toimplement functions to support the PDSM. A first example functionincludes continually measuring the parametric data of ports and channelsof the instrument module. A second example function includes obtainingall of the parametric data measurements for input signal(s) and sortingthose parametric data measurements into types—e.g., into parametriccomponents A and B of FIG. 2. Once sorted, the parametric datameasurements are encapsulated in PCIe formatted packets and sent to thebackplane over an appropriate serial bus. A third example functionincludes receiving, per port and per channel, parametric data from thebackplane and applying the individualized parametric data to thecorresponding port and channel within the instrument module.

In some implementations, the PDSM on the backplane, on an ongoing basis,receives and decodes high-speed serial data from each of the instrumentmodules connected to the backplane, or a subset thereof. The PDSMmultiplexes the received data serially back to the appropriatemodule(s).

In some implementations, an active control loop between communicationchannels is configured to stabilize and to provide an optical signalhaving desired parametric characteristics. For example, in someimplementations, the active control loop may be a power control loop toprovide an output optical signal having a stable, and defined, opticalpower level. Notably, however, the active control loop is not limited toproviding an optical signal having power characteristics. Rather, theactive control loop may be configured to provide an output opticalsignal having any one or more parametric characteristics including, butnot limited to, a specified optical power, signal-to-noise ratio,modulation amplitude, extinction ratio, wavelength, rise time, falltime, slew rate, or any other characteristic relating to a wave or thewave's shape.

FIG. 4 shows an example implementation of an active control loop 60 forcontrolling parametric data transfers between two communicationchannels. In some implementations, the active control loop may beconfigured to stabilize parametric data at the output (e.g., toeliminate or reduce spikes or noise in the parametric data) Activecontrol loop 60 is a represented conceptually by a dashed curve havingan arrow that shows an example direction of control/data flow.

FIG. 4 shows only two example communication channels; however, theactive control loop described herein may be implemented among more thantwo communication channels, as appropriate. The communication channelsmay include an input channel 61 and an output channel 62, although thechannels may be two input channels or two output channels, as describedbelow. In some implementations, the input channel includes circuitryconfigured to receive an optical signal, to convert the optical signalto an electrical (e.g., a digital) signal, to obtain parametricinformation about the optical signal before, during, or after theconversion process, and to obtain parametric data based on theinformation (e.g., to generate digital data representing the parametricinformation). In an example, the parametric information may be measuredby an interface circuit and converted to digital data by the interfacecircuit or other appropriate logic. In some implementations the outputchannel includes circuitry configured to receive an electrical (e.g., adigital) signal, to convert the electrical signal to an optical signal,to obtain parametric information about the optical signal before,during, or after the conversion process, and to obtain parametric databased on the information (e.g., to generate digital data representingthe parametric information). In an example, the parametric informationmay be measured by an interface circuit and converted to digital data bythe interface circuit or other appropriate logic.

In the example of FIG. 4, channel 61 includes an optical input port 64comprising an interface configured to receive an optical signal 66, andto generate informational content data 67 representing the informationalcontent of the optical signal. Input port 66 is also configured tomeasure parametric information for the optical signal, such as, but notlimited to, optical power level, signal-to-noise ratio, modulationamplitude, extinction ratio, wavelength, rise time, fall time, slewrate, or any other characteristic relating to a wave or the wave'sshape. In this example, the parametric information represents theoptical power level of the optical signal; however, as noted, theparametric information may represent any appropriate parametriccharacteristic of the optical signal. In this example, channel 61 alsoincludes an analog-to-digital converter (ADC) 69. ADC 69 receives themeasured parametric information 70, and converts that information intodigital data; that is, parametric data 71. Thus, the input port and ADCcapture the parametric data, and forward that parametric data tomultiplexers of the type shown in FIG. 2 (e.g., 38, 39, 40) onprogrammable logic, such as an FPGA 73.

In the example of FIG. 4, memory 74 stores calibration data, e.g.,parameter values, that may be used to calibrate the parametric data. Thecalibration data may be specific to the input port, and may be used tocorrect for errors produced by the input port. For example, the inputport may include a photodiode. The photodiode may have physical oroptical characteristics that cause it to operate in a way other thanexpected, particularly at different temperatures, resulting inparametric information (and, thus, parametric data) containing an errorcomponent. Calibration may be performed to correct for errors other thanerrors produced by the photodiode. The calibration data may be appliedto the parametric data via logic in the FPGA to correct for this errorcomponent. An example of error correction of parametric data isdescribed below with respect to output channel 62.

As described above with respect to FIGS. 2 and 3, DDSM 75 transmitsinformational content data between channels 61 and 62, and PDSM 76transmits parametric data between channels 61 and 62. As shown in FIG.4, DDSM 75 transmits the informational content data to output port 77.PDSM 76 transmits the parametric data 80 to output circuitry 78, whichis located on a path of the output channel. In an example, theparametric data may be, or may be based on, the parametric data that wasobtained from the optical signal at channel 61. In some implementations,the parametric data may be independent of the parametric data forchannel 61 and may be provided to output circuitry 78 from a sourceunrelated to channel 61. For example, parametric data 79 may beprogrammed into the system, e.g., by the host computing system, and maybe provided to the output circuitry from there. Such parametric data maybe defined by a user to control the target parameter(s) (e.g., opticalpower level) of the output signal. In some implementations, parametriccircuitry other than the PDSM described herein or the hardware used toprovide the programmatic inputs may be used.

In the example of FIG. 4, output circuitry 78 includes programmablelogic 81, which may be an FPGA or other appropriate programmable device.In some implementations, the functionality implemented therein describedbelow may be implemented using discrete logic components, an ASIC, orother appropriate circuitry.

Output circuitry 78 includes a selector circuit 82, such a multiplexer,to select between the parametric data 80 provided by PDSM 76 or theparametric data 79 provided via programmatic (or other) input. Selectionmay be controlled by one or more processing devices that are either on,or off, the backplane. For example, selection may be controlled by thehost computing system of FIG. 1 or using input(s) from the hostcomputing system. The selected parametric data is the parametric datathat is usable by the output circuitry to produce an optical signalhaving the informational content of the informational content data 67and the parametric characteristics of the selected parametric data(either parametric data based on parametric data obtained from channel61 or parametric data otherwise specified, e.g., programmatically).

In the example of FIG. 4, the output circuitry includes an errorcorrection loop 83 to calibrate, e.g., to correct, for errors introducedby hardware in the output port or elsewhere, such as a photodiode. Errorcorrection loop 83 is a feedback loop represented conceptually by adashed ellipse having an arrow that shows the direction of feedback. Insome implementations, however, this internal error correction loop maybe omitted. In example implementations like this, the selectedparametric data and the informational content data are both provideddirectly to the output port 77. The output port then generates anoptical signal 84 having the informational content of the informationalcontent data and the parametric characteristics of the selectedparametric data.

The example of FIG. 4, however, includes error correction loop 83. Inthis example, the error correction loop comprises a proportional,integral, derivative control loop configured to calculate an error value(“err”) of the output optical signal based as a difference between atarget output parametric characteristic (e.g., a predefined opticalpower) and a measured parametric characteristic (e.g., a measuredoptical power), and to apply a correction to the output optical signalbased on that error. For example, memory 85 may store calibration data(e.g., parameter values) that are usable to correct for hardware, orother, errors in the output circuitry, such as photodiode-introducederrors in output port 77. The selected parametric data and thecalibration data 86 are summed via an adder (“Σ”), and the resultingerror (“err”) applied to proportional (P), integral (I), and derivative(D) components. Each of these components produces an output, which aresummed via another adder (“Σ”). The resulting sum 88 constitutes controldata that, in this example, is converted into an analog signal 89 bydigital-to-analog controller (DAC) 90. This analog signal is a correctedparametric control voltage that is used by the output port to producethe optical signal having parametric characteristics reflecting theselected parametric data as corrected for any errors introduced bysignal-generating hardware or other factors, such as temperature.

The error control loop incorporates output port 77. In someimplementations, optical output port 77 may comprise an interfaceconfigured to receive an electrical signal (informational content data67), to receive a signal representing the selected parametric data ascorrected, and to generate an optical signal 84 representing theinformational content of the electrical signal and having parametriccharacteristics based on the selected parametric data. In someimplementations, output port 77 is also configured to measure parametricinformation for the output optical signal, such as, but not limited to,optical power level, signal-to-noise ratio, modulation amplitude,extinction ratio, wavelength, rise time, fall time, slew rate, or anyother characteristic relating to a wave or the wave's shape. In thisexample, the measured parametric information 91 represents the opticalpower level of the optical signal; however, as noted, the parametricinformation may represent any appropriate parametric characteristic ofthe optical signal. In this example, channel 62 also includes ananalog-to-digital converter (ADC) 94. ADC 94 receives the measuredparametric information 91, and converts that information into digitaldata 95; that is, parametric data. Thus, output port 77 and ADC 94capture the parametric data, and forward that measured parametric dataas an input 94 of the error correction loop 83.

Input 94 receives the measured parametric data 95 and adjusts themeasured parametric data based on the calibration data 86 received frommemory 85. The result is then combined with the selected parametric datato produce an error (“err”) value, and the process described above isrepeated to continually correct for error in the output signal relativeto a target output. In some implementations, error correction of thistype may be used to stabilize output power, and to smooth-out spikes ornoise in output power that may be present in the parametric data.

In the example of FIG. 4, the active control loop described is describedwith respect to an input port 64 and an output port 77. However, theactive control loop may be used with any two or more ports tocommunication channels. For example, the active control loop may be usedto control the parametric characteristics of one channel (input oroutput channel) based on the parametric characteristics of any one otherchannel (input or output channel). In some implementations, multipleactive control loops may be used to control the parametriccharacteristics of multiple channels (input or output channel) based onthe parametric characteristics of any one other channel (input or outputchannel). In some implementations, multiple active control loops may beused to control the parametric characteristics of one channel (input oroutput channel) based on the parametric characteristics of multipleother channels (input or output channel). For example, a single channelmay produce a signal having the optical power of one channel and thewavelength of another, different channel using two active control loopsencompassing the single channel and the two other channels.

In some implementations, the active control loops may be used toimplement margin testing, as described herein. For example, a user mayspecify programmatically that the output power levels are always −5 dBmin one application. In another application, the user may specifyprogrammatically that the output power level should always be 2 dB lessthan the power on another channel. These example power characteristicsmay be controlled by providing, and selecting, appropriate parametricdata, as described above.

In some implementations, all or part of the switching circuitry isconfigured to support AC (alternating current)-coupled data having afrequency that is greater than or equal to one or more minimumpredefined frequencies. For example, all or part of the switchingcircuitry may be configured to operate with AC data only, and not tooperate with direct current (DC) data. In some implementations, the DDSMmay be configured to operate only with AC data having a frequencygreater than a minimum predefined frequency. In some implementations,the PDSM may be configured to operate only with AC data having afrequency greater than a minimum predefined frequency. In someimplementations, both the DDSM and the PDSM may be configured to operateonly with AC data having a frequency greater than a minimum predefinedfrequency. The minimum frequencies at which the DDSM and/or the PDSM mayoperate may be the same or different frequencies, and may have anyappropriate value(s).

Circuitry is described herein to enable use of the switching circuitry,and thus the system, with data having frequencies lower than the minimumfrequency supported by the switching circuitry. For example, signals maybe received on a communication channel. The signals may be optical orelectrical. The signals may be received by input circuitry whichobtains, from the signals, both informational content data representingthe informational content of those signals and parametric datarepresenting the non-informational signal content of the signals. Theinformational content data and/or the parametric data may each have anoriginal frequency that is less than the minimum frequency supported bythe switching circuitry. Accordingly, the system includes circuitry toencode the informational content data and/or the parametric data so thateach has a frequency that is greater than or equal to the minimumpredefined frequency supported by the switching circuitry. In someimplementations, the original frequency and the frequency producedthrough sampling are both non-zero AC frequencies. In someimplementations, the original frequency is zero (e.g., the originalsignal may be a DC signal), and the frequency produced through samplingis a non-zero AC frequency. FIG. 5 shows an example implementation ofthe circuitry described above. In this example, the circuitry includescircuitry 100 configured to obtain data corresponding to input opticalor electrical signals (e.g., an “input signal”) on communication channel101. In some implementations, the circuitry is configured to convert theinput signals to informational content data. In some implementations,the circuitry is configured to receive, from communication channel 101,informational content data having the frequency (or data rate) that isless than the minimum predefined frequency. Referring to FIG. 4, in someimplementations, circuitry 100 may include all, or part of, input port64, FPGA 73, and/or ADC 69 for performing the receiving and/orconverting functions; however, in other implementations circuitry 100may include different input circuitry. In some implementations,circuitry 100 also includes sampling circuitry. In the example of FIG.5, the sampling circuitry is configured to sample the obtainedinformational content data and parametric data to produce encodedinformational content data 103 and encoded parametric data 104. In someimplementations, the sampling circuitry may be configured to sample theinformational content data to produce encoded informational content dataonly, or to sample the parametric data to produce encoded parametricdata only. In some implementations, the parametric data changes slowly,so it is encoded in the system. In some implementations, the parametricdata is sampled at a relatively low data rate and transferred at arelatively high data rate. In the example of FIG. 5, the encodedinformational content data 103 and the encoded parametric data 104 eachhave a frequency that is greater than or equal to the minimum predefinedfrequency (e.g., at least as great as the frequency) supported by theswitching circuitry. In some implementations, the frequency of theencoded informational content data 103 is the same as the frequency ofthe encoded parametric data 104. In some implementations, the frequencyof the encoded informational content data 103 is different from thefrequency of the encoded parametric data 104. In some implementations,the frequency of the encoded informational content data 103 is greaterthan the frequency of the encoded parametric data 104. In someimplementations, the frequency of the encoded informational content data103 is less than the frequency of the encoded parametric data 104.Referring to FIG. 4, in some implementations, the sampling performed bycircuitry 100 may be performed by input port 64, ADC 69, and FPGA 73.For example, input port 64 may be configured to sample the originalinput signal to produce the encoded informational content data, and ADC69 and/or FPGA may be configured to sample parametric data of theoriginal input signal to produce the encoded parametric data. In someimplementations, input port 64 may be configured to sample parametricdata of the original input signal to produce the encoded parametricdata.

In the example of FIG. 5, switching circuitry 105 includes DDSM 107 andPDSM 108. However, as explained elsewhere herein, in someimplementations, the switching circuitry may include circuit componentsother than, or in addition to, the DDSM and the PDSM. In the example ofFIG. 5, the DDSM is configured to receive, and to route, the encodedinformational content data 103 in the manner described herein. Forexample, the DDSM is configured to forward the encoded informationalcontent data 103 on a path 110 to communication channel 120 (the outputcommunication channel in this example). In the example of FIG. 5, thePDSM is configured to receive, and to route, the encoded parametric data104 in the manner described herein. For example, the PDSM is configuredto forward the encoded parametric data on a path 112 to communicationchannel 120. In some implementations, the encoded informational contentdata is transmitted through the path to the switching circuit at afrequency greater than or equal to the frequency supported by the pathand/or the switch.

In the example of FIG. 5, both the encoded parametric data and theencoded informational content data are forwarded to output circuitry114, and are used by output circuitry 114 to produce the reconstructedsignal. In some implementations, output circuitry 114 may have theconfiguration of output circuitry 78 of FIG. 4. In some implementations,output circuitry 114 may have a different configuration than thatdescribed herein. Referring to FIG. 4, the encoded informational contentdata may be represented by reference 67 and the encoded parametric datamay be represented by reference 80. As described with respect to FIG. 4,a selector circuit 82, such a multiplexer, is configured to selectbetween the encoded parametric data 80 provided by the PDSM or theparametric data 79 provided via programmatic (or other) input. Selectionmay be controlled by one or more processing devices that are either on,or off, the backplane. For example, selection may be controlled by thehost computing system of FIG. 1 or using input(s) from the hostcomputing system. The selected parametric data is the parametric datathat is usable by the output circuitry 114 to produce an output optical(or electrical) signal having the informational content of theinformational content data 67 and the parametric characteristics of theselected parametric data (either parametric data based on parametricdata from the PDSM or parametric data otherwise specified, e.g.,programmatically).

In the example of FIG. 5, and as described with respect to FIG. 4, theoutput circuitry may be controlled to produce a “reconstructed signal”on channel 120 based on the encoded informational content data and theencoded parametric data. For example, output circuitry 114 may decodeboth the encoded informational content data and the encoded parametricdata, which may result in informational content data and parametric datahaving the frequencies that are less than the minimum predefinedfrequency supported by the switching circuitry. This may be because thecomponents used in the communication or the switching circuitry itselfis AC-coupled. In some implementations, the frequency of the resultinginformational content data is the same as the frequency of the resultingparametric data. In some implementations, the frequency of the resultinginformational content data different from the frequency of the resultingparametric data. In some implementations, the frequency of the resultinginformational content data is greater than the frequency of theresulting parametric data. In some implementations, the frequency of theresulting informational content data is less than the frequency of theresulting parametric data. In some implementations, decoding may beperformed by output port 84, FPGA 81, and/or DAC 90. For example, insome implementations, output port 77 may be configured to decode theencoded parametric data and to decode the encoded informational contentdata. In some implementations, FPGA 81 and/or DAC 90 may be configuredto decode the encoded parametric data to produce the resultingparametric data.

In some implementations, the reconstructed signal is the same, bothinformationally and parametrically, as the original input signal oncommunication channel 101. That is, the informational content data isused to replicate the informational content of that original inputsignal, and the parametric data is used to replicate thenon-informational content of that original input signal. As describedherein, in some implementations, the reconstructed signal may be formedusing the informational content data of the original input signal andother (e.g., programmed) selected parametric data, resulting in areconstructed single having the same informational content as theoriginal input signal, but different parametrics. In someimplementations, as described herein, the reconstructed signal may beformed using informational content data obtained from a communicationchannel other than communication channel 101, and using parametric datafrom communication channel 101. As a result, the reconstructed signalmay have information content different from that of the original inputsignal, but parametrics that are the same as the parametrics of theoriginal input signal (decoded from the encoded parametric data 104).

In some implementations, the DDSM may support a minimum data rate of 1Mb/s (megabit-per-second). A UUT may, however, require low-speedapplications from DC to 1 kb/s (kilobits-per-second), for example. Inthis example, the system may encode the input signal at a data rate thatis supported by the DDSM, and may transfer the encoded digital signal tothe DDSM. That data is then decoded to reconstruct the original inputsignal on the output channel. The parametric data can also be encoded,transmitted, and used to reconstruct the parametric components of thesignal as described herein.

In some implementations of the circuitry described herein, multipleoptical transmission media (e.g., multiple optical fibers) may be usedto provide at least informational content to a single electricaltransmission medium (e.g., a wire). In some implementations of thecircuitry described herein, multiple optical transmission media may beused to receive at least informational content from a single electricaltransmission medium. In some implementations of the circuitry describedherein, multiple electrical transmission media (e.g., multiple wires)may be used provide at least informational content to a single opticaltransmission medium (e.g., an optical fiber). In some implementations ofthe circuitry described herein, multiple electrical transmission mediamay be used to receive at least informational content from a singleoptical transmission medium. In some implementations of the circuitrydescribed herein, the same circuitry may include one or more opticaltransmission media and one or more electrical transmission media toprovide at least informational content to a single electricaltransmission medium. In some implementations of the circuitry describedherein, the same circuitry may include one or more optical transmissionmedia and one or more electrical transmission media to receive at leastinformational content from a single electrical transmission medium. Insome implementations of the circuitry described herein, the samecircuitry may include one or more optical transmission media and one ormore electrical transmission media to provide at least informationalcontent to a single optical transmission medium. In some implementationsof the circuitry described herein, the same circuitry may include one ormore optical transmission media and one or more electrical transmissionmedia to receive at least informational content from a single opticaltransmission medium.

In the examples described herein, processing of data is performed in theelectrical domain. However, in some implementations, all or part of theprocessing maybe be performed in the optical domain using appropriateoptical circuitry.

The system and features described herein may be implemented as, or bepart of, automatic test equipment (ATE). ATE refers to an automated,usually computer-driven, system for testing devices. ATE typicallyincludes a computer system, such as that shown in FIG. 1, and one ormore instrument modules (e.g., as shown in FIG. 1) or a single devicehaving corresponding functionality. In an example operation, in responseto instructions in a test program set (TPS), some ATE automaticallygenerates input signals to be applied to a UUT, and monitors outputsignals from the UUT. In some implementations, pin electronics in theATE compares the received output signals with expected responses (e.g.,threshold) to determine whether the UUT is defective or has passed atest. In an example, an instrument module outputs voltage and/or currentto the UUT, and receives voltage and/or current from the UUT. Forexample, in some implementations, ATE may be capable of forcing voltageto a UUT and sourcing current to the UUT. In some implementations, theATE is capable of providing test signals to a UUT, receiving responsesignals from the UUT, and forwarding those response signals forprocessing to determine whether the UUT meets testing qualifications.Signals are transmitted between the ATE and the UUT over thecommunication channels described herein. The test and response signalsmay be processed as described herein, e.g., to identify theirinformational and parametric content, to distribution data representingthe informational and parametric content, and so forth.

In some implementations, test signals may be sent over multiple channelsand test results may be based on response signals received from multiplechannels. In some implementations, test signals may be sent over asingle channel and test results may be based on response signalsreceived from a single channel. In some implementations, test signalsmay be sent over a multiple channels and test results may be based onresponse signals received from a single channel. In someimplementations, test signals may be sent over a single channel and testresults may be based on response signals received from multiplechannels. The circuitry described herein may be programmed, e.g., by auser at a host computing system or a test program set to send testsignals over, and receive response signals from, a single channel ormultiple channels as desired.

In general, the circuitry described herein for generating opticalsignals for output may include any appropriate device, such as one ormore lasers or light-emitting diode(s) (LEDs) or a vertical-cavitysurface-emitting laser (VCSEL).

Testing performed using the example systems described herein may beimplemented using hardware or a combination of hardware and software.For example, a system like the ones described herein may include variouscontrollers and/or processing devices located at various points in thesystem to control operation of the automated elements. A centralcomputer may coordinate operation among the various controllers orprocessing devices. The central computer, controllers, and processingdevices may execute various software routines to effect control andcoordination of the various automated elements.

The techniques described herein may be performed by systems or any otherappropriate computing device. The techniques can be controlled, at leastin part, using one or more computer program products, e.g., one or morecomputer program tangibly embodied in one or more information carriers,such as one or more non-transitory machine-readable media, for executionby, or to control the operation of, one or more data processingapparatus, e.g., a programmable processor, a computer, multiplecomputers, and/or programmable logic components.

A computer program can be written in any form of programming language,including compiled or interpreted languages, and it can be deployed inany form, including as a stand-alone program or as a module, component,subroutine, or other unit suitable for use in a computing environment. Acomputer program can be deployed to be executed on one computer or onmultiple computers at one site or distributed across multiple sites andinterconnected by a network.

Actions associated with implementing all or part of the testing can beperformed by one or more programmable processors executing one or morecomputer programs to perform the functions described herein. All or partof the testing can be implemented using special purpose logic circuitry,e.g., an FPGA (field programmable gate array) and/or an ASIC(application-specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only storagearea or a random access storage area or both. Elements of a computer(including a server) include one or more processors for executinginstructions and one or more storage area devices for storinginstructions and data. Generally, a computer will also include, or beoperatively coupled to receive data from, or transfer data to, or both,one or more machine-readable storage media, such as mass storage devicesfor storing data, e.g., magnetic, magneto-optical disks, or opticaldisks. Machine-readable storage media suitable for embodying computerprogram instructions and data include all forms of non-volatile storagearea, including by way of example, semiconductor storage area devices,e.g., EPROM, EEPROM, and flash storage area devices; magnetic disks,e.g., internal hard disks or removable disks; magneto-optical disks; andCD-ROM and DVD-ROM disks.

Any “electrical connection” or “optical connection” as used herein mayimply a direct physical connection or a wired or wireless connectionthat includes or does not include intervening components but thatnevertheless allows signals to flow between connected components. Any“connection” involving electrical circuitry or optical componentsmentioned herein that allows signals to flow between two points, unlessstated otherwise, is not necessarily a direct physical connectionregardless of whether the word “electrical” or “optical” is used tomodify “connection”. Elements of different implementations describedherein may be combined to form other embodiments not specifically setforth above. Elements may be left out of the structures described hereinwithout adversely affecting their operation. Furthermore, variousseparate elements may be combined into one or more individual elementsto perform the functions described herein.

What is claimed is:
 1. A system comprising: input circuitry to obtainfirst data corresponding to first signals on a communication channel,the first data having a first frequency that is less than a predefinedfrequency; sampling circuitry to sample the first data to produce seconddata having a second frequency that is greater than or equal to thepredefined frequency; switching circuitry to support AC-coupled datahaving a frequency that is greater than or equal to the predefinedfrequency, the switching circuitry being configured to receive thesecond data and to forward the second data; and output circuitry toreceive the second data and parametric data representing non-informationsignal content, to produce third data based on the second data, and toproduce, based on the third data and the parametric data, second signalsfor output from the system.
 2. The system of claim 1, wherein thesampling circuitry is configured to encode the first data at the secondfrequency to produce the second data; and wherein the output circuitryis configured to decode the second data to produce the third data. 3.The system of claim 2, wherein the third data has a third frequency thatis less than the predefined frequency.
 4. The system of claim 3, whereinthe third frequency is the same as the first frequency.
 5. The system ofclaim 1, wherein the parametric data represents non-informational signalcontent of the first signals; wherein the sampling circuit is configuredto encode the parametric data at a third frequency that is greater thanor equal to the predefined frequency to produce encoded parametric data;wherein the switching circuit is configured to receive the encodedparametric data, and to forward the encoded parametric data to theoutput circuitry; and wherein the output circuitry is configured todecode the encoded parametric data to produce the parametric data, theparametric data having a fourth frequency that is less than thepredefined frequency.
 6. The system of claim 1, wherein the switchingcircuitry comprises: a first switch to receive the second data and toforward the second data to the output circuitry; and a second switch toreceive the parametric data and to forward the parametric data to theoutput circuitry, the parametric data representing non-informationalsignal content of the first signals.
 7. The system of claim 6, whereinthe first switch and the second switch are controllable independently.8. The system of claim 1, wherein the switching circuitry comprises afirst switch to receive the second data and to forward the second datato the output circuitry; and wherein the output circuitry comprises aselector circuit to receive the parametric data from a source other thanthe switching circuitry, and to select the parametric data for use bythe output circuitry to produce the third data.
 10. The system of claim1, wherein the second signals are identical to the first signals bothinformationally and parametrically.
 11. The system of claim 1, whereinthe first frequency and the second frequency are each non-zero ACfrequencies.
 12. The system of claim 1, wherein the first frequency iszero and the second frequency is a non-zero AC frequency.
 13. A methodcomprising: obtaining first data corresponding to first signals on acommunication channel, the first data having a first frequency that isless than a predefined frequency; sampling the first data to producesecond data having a second frequency that is greater than or equal tothe predefined frequency; receiving, at switching circuitry, the seconddata and forwarding the second data, the switching circuitry beingconfigured to support AC-coupled data having a frequency that is greaterthan or equal to the predefined frequency; producing third data based onthe second data; and producing, based on the third data and theparametric data, second signals for output.
 14. The method of claim 13,sampling comprises encoding the first data at the second frequency toproduce the second data; and wherein producing the third data comprisesdecoding the second data.
 15. The method of claim 14, wherein the thirddata has a third frequency that is less than the predefined frequency.16. The method of claim 15, wherein the third frequency is the same asthe first frequency.
 17. The method of claim 13, wherein the parametricdata represents non-informational signal content of the first signals;wherein sampling comprises encoding the parametric data at a thirdfrequency that is greater than or equal to the predefined frequency toproduce encoded parametric data; wherein the switching circuit receivesthe encoded parametric data, and forwards the encoded parametric data tothe output circuitry; and wherein the method comprises decoding theencoded parametric data to produce the parametric data, the parametricdata having a fourth frequency that is less than the predefinedfrequency.
 18. The method of claim 13, wherein the switching circuitrycomprises: a first switch to receive the second data and to forward thesecond data to the output circuitry; and a second switch to receive theparametric data and to forward the parametric data to the outputcircuitry, the parametric data representing non-informational signalcontent of the first signals.
 19. The method of claim 18, wherein thefirst switch and the second switch are controlled independently.
 20. Themethod of claim 13, wherein the second signals are based on the firstsignals both informationally and parametrically.
 21. The method of claim13, wherein the first frequency and the second frequency are eachnon-zero AC frequencies.
 22. The method of claim 13, wherein the firstfrequency is zero and the second frequency is a non-zero AC frequency.